Recent emphasis has been placed upon compact reflectometers that can be used directly by the patient as a blood analyzer. Particularly such reflectometers are needed by diabetics who take repeated measurements of the glucose levels of their whole blood. Most properly, such reading should be taken at regular intervals, wherever the patient finds himself. This is not possible unless the reflectometer is readily portable. Portability requires more than just being lightweight or small--the bulk and shape also dictate whether the reflectometer is convenient to carry. A truly portable and convenient reflectometer would be one which would fit, for example, in the patient's shirt or coat pocket. Preferably, such a reflectometer should not be thicker than 2 cm.
Commonly owned, copending application Ser. No. 401,754 filed by J. W. Ward on July 26, 1982, and entitled "Light Guide Reflectometer" describes a reflectometer featuring a light guide one interior surface of which acts as a mirror to reflect light from a light source to the horizontally supported test element. Such mirrored surface allows the light source to be displaced at an angle to, that is, to one side of, the normal to the test element, thereby permitting some reduction in thickness. However, because the conventional approach has been to "read" the element by detecting radiation diffusely reflected at 90.degree. from the test element, the detector of necessity was placed under the test element. That is, it is conventional to direct incoming light at an angle of 45.degree. to the test element, and to detect diffusely reflected light at an angle of 90.degree. thereto, i.e., normal to the plane. This angular arrangement eliminates detection of specular reflection, namely that which is reflected at 45.degree.. However, such an optical arrangement dictates the placement of the photodetector directly opposite to the supported test element. Although commercially available inexpensive detectors now have a reduced thickness, they still have an appreciable thickness that adds to the thickness of the photometer if the detectors are placed under the examined test element. The added thickness detracts from portability.
However, portability is not the only requirement. The reflectometer must be one that is otherwise convenient to use, to insure that it will be used as often as is required. Pocket-sized reflectometers have been provided with convenient thicknesses by constructing the axes of the light source and detector to be generally parallel to the planes of the major exterior surfaces (see for example, those described in the owner's Manual of the "Glucoscan" analyzer, published in 1982 by Lifescan). However, those reflectometers feature a test element that is oriented vertically when the reflectometer is placed in its normal resting position. Such vertical orientation has disadvantages, since any excess blood or serum sample on the absorbing pad of the test element will run off into the reflectometer and provide possible contamination. As a result, the patient must either blot off the excess, or wait until it is fully absorbed. In either case, the patient experiences an inconvenience. Also reflectometers such as the "Glucoscan" described above require the test element to be properly aligned with a thin, small slot in order to insert the pad into the reflectometer. This can be a difficulty for elderly or infirm patients.
Thus there has been a need, prior to this invention, for a compact reflectometer that is adapted to read a test element supported in a generally horizontal orientation, and particularly one that so supports the element on a readily accessible support surface.